Hormonal Mechanism

Peptide/Protein Hormones: Water-soluble. Bind to membrane receptors, do not enter the cell, generate secondary messengers (cAMP, IP3, Ca2+) to alter cellular metabolism; Steroid/Iodothyronines: Lipid-soluble. Enter the cell, bind to intracellular receptors (often in the nucleus), and regulate gene expression/chromosome function to produce physiological responses.